DECOMPOSITION OF MN-C DIPOLES DURING QUENCH-AGING IN LOW-CARBON ALUMINUM-KILLED STEELS

Variations in electrical resistivity and the deviation from Matthiessen's rule (DMR) during quench-aging have been observed on steels containing varied amounts of manganese at 273 K and liquid-nitrogen temperature. During the period of violent precipitation of iron-carbides (unidentified carbide, epsilon carbide and cementite), the DMR decreases in steel containing 0. 1 mass% Mn whereas it increases in steels containing 0. 4 mass%, 0. 8 mass% and 1. 2 mass% Mn. For the latter three steels, the higher the manganese content, the more marked the increase in DMR. It is deduced that the decomposition of quenched-in Mn-C dipoles occurs simultaneously with the precipitation of carbides. It is speculated that the solubility of single carbon atoms in ferrite in equilibrium with cementite at 973 K decreases gradually with increasing manganese content, whereas the total amount of carbon atoms contained in ferrite at 973 K, including those combined with manganese atoms to form Mn-C dipoles, increases with increasing manganese content. The binding energy of a carbon atom with a manganese atom is evaluated to be 7. 4 multiplied by 10** minus **2**0 J (0. 46 ev).